Extract the bioenergy immediately and return the nutrients with the ashes
The production rate in the forest for both round timber and biofuel can be increased. That’s the conclusion of a conference on forest residues at the Elmia Wood international forestry fair in Jönköping, Sweden.
Conference participants included researchers from the Swedish University of Agricultural Sciences and the Forestry Research Institute of Sweden (Skogforsk) plus representatives of the Swedish Forest Agency, a government authority which monitors and ensures that Swedish forests are managed in a sustainable way.
Hillevi Eriksson, an expert on environmental effects with the Swedish Forest Agency, says that the Swedish forest industry is doing a relatively good job at the moment. However, there are concerns that the increased dual usage of the forests as a supplier of both industrial raw materials and biofuel can lead to problems.
“We’ve already seen examples where insufficient residue has been left in the forest,” she says.
Lack of knowledge
Swedish forestry is thus under the watchful gaze of the government. However, researchers say it is possible to increase production without causing any negative environmental impact. The key is to have a systemized approach. Gunnar Thelin from the Swedish forest consultancy Ekobalans, which works with issues of fertilizing and soil conservation, says the production of biomass is more complicated than the production of round timber.
The problem today is a lack of knowledge, both among the people who are working in the forest and at the systems level. According to Maria Ivarsson Wide of the Forestry Research Institute of Sweden (Skogforsk), the biofuel industry is now at the same stage as traditional forestry was when it was first mechanized.
Another problem is that forest owners and industry regard bioenergy as an obstacle to production. The current practice is that branches and tops should be left lying in the forest for a year so that their needles fall. The needles contain a large proportion of the nutrients that must be returned to the soil. This practice delays replanting and means that a couple of years’ growth is lost. But things don’t have to be this way.
Needles aren’t necessary
“The majority of the needles just disappear anyway or they lie in heaps where the residues were stored,” explains Gustaf Egnell from the Swedish University of Agricultural Sciences. “We might just as well make use of the residues at the same time as the round timber and replant immediately.”
This advice is valid as long as the nutrients are returned to the forest in another way, as Gunnar Thelin pointed out. This can be achieved by spreading the ashes produced by the burning of pure forest fuel. The ashes contain minerals and other nutrients that are needed to maintain the nutrient balance in the soil.
“We need to return a lot more ash than we’re doing today,” Gunnar says. “How much, depends on the type of soil, but in southern Sweden it would be five to ten tonnes per hectare.”
Ash by itself is not a stand-alone fertilizer, but as Rolf Björheden from the Forestry Research Institute of Sweden pointed out, it is not difficult to mix in the other nutrients required when you are spreading the ash anyway.
Stand cleaning and stumps
In Sweden there are two unexploited energy sources in the forest: uncleaned forest areas and stumps. More than a million hectares are believed to be in acute need of cleaning, but so far there is no economically viable harvesting method. However, Maria Ivarsson Wide says there is a solution in sight. It involves using harvesting heads that can process entire bunches of small-diameter trees, a process known as accumulation. Studies by the Forestry Research Institute of Sweden show that the technology to do this is within reach.
Harvesting stumps involves similar methodological problems but with additional environmental issues such as the risk of worsening the load capacity of the ground, increasing soil erosion, and more leakage of nutrients, heavy metals and other substances to the surface water. Research into these problems is continuing and it is possible to solve them.
In conclusion: Biofuel does not have to be an obstacle to forestry operations; on the contrary, it can contribute to a better economy for everyone involved. One possibility is to collect the forest residues at the same time as felling the trees, begin replanting immediately, and return the nutrients by spreading the ash complemented by the addition of other nutrients. This approach would also increase tree growth in the forests.